Neutral setting device for an adjustable hydraulic machine

ABSTRACT

The invention relates to a neutral setting device of an adjustable hydraulic machine, in particular the adjustment of the neutral setting of a servo valve. The present invention relates in particular to servo adjustment devices with mechanically adjustable control pistons, wherein the necessary force can be applied mechanically, electromagnetically, pneumatically or hydraulically. The invention relates to a neutral setting device of an adjustable hydraulic machine with a housing in which a mounted input shaft is arranged, at which on one end a torque can be applied for turning the input shaft around an axis. On a second end a cylindrical extension is arranged eccentrically parallel to the axis. An adjustable control piston for opening and closing hydraulic fluid openings for application of pressure of a servo piston adjusts the hydraulic machine with respect to its delivery volume.

The invention relates to a neutral setting device of an adjustable hydraulic machine in accordance with the preamble of Claim 1. The invention relates in particular to the adjustment of the neutral setting of a servo valve. The invention relates in particular to hydrostatic adjustment devices of hydraulic machines in which case both the delivery volume and the delivery direction are adjustable. The present invention relates in particular to servo adjustment devices with mechanically adjustable control pistons, wherein the forces necessary for this purpose can be applied mechanically, electromagnetically, pneumatically or hydraulically. A generic device is known from DE 41 25 706 C1, whose features constitute the preamble of Claim 1.

Hydraulic servo valves are used in variable designs for the adjustment of the delivery volume of hydraulic pumps. In the process a servo piston is controlled via such a servo valve with hydraulic fluid or has hydraulic pressure applied so that the servo piston adjusts the actual adjustment device of the hydraulic machine, such as for example the swash plate of an axial piston machine. The invention can be used for servo valves of this type. Additional fields of application are for example the control of radial piston machines whose eccentricity is adjustable, or for example bent axis pumps which can be modified in their power or also delivery direction by deflection of a burden. Normally the servo pistons which act on the adjustment devices of the hydraulic machines are centered via springs in their zero position, as a result of which in the case of balanced pressure conditions for example on a double-sided servo piston, the delivery flow of the hydraulic machine is zero. This is also known from the generic device according to DE 41 25 706 C1, whose features constitute the preamble of Claim 1.

The delivery volume zero corresponds to machine downtime, i.e. the hydraulic machine neither receives power nor emits it. This machine downtime is of safety significance and must therefore be precisely definable by the servo valve device. The control piston in the servo valve responsible for the pressures on the servo piston controls the respective hydraulic pressures to the servo piston or pistons via its control edge, which is why the hydraulic neutral position of the control piston in the control cylinder, thus its position for the machine downtime of the hydraulic machine necessarily must be precisely adjustable.

However, in practice both the control piston in its diameter and its control edges as well as the control cylinder in its diameter and its corresponding control edges are subject to tolerances in production, as a result of which the neutral position of the control piston in the control cylinder usually deviates from the constructive predefined central position or the geometrically centered location. Thus if one wants to strictly geometrically center the control piston of a servo valve in the control cylinder of the servo valve, an asymmetrical application of pressure of for example a two-sided servo piston cannot be ruled out. As a result of this the servo piston moves and the adjustable hydraulic machine would be outside of the zero position and machine downtime could not be achieved. Hence a mechanism for neutral setting is necessary to compensate the position error of the control piston in the control cylinder caused by production tolerances so that the hydraulic machine facilitates the zero position of the servo piston in the hydraulic neutral position of the control piston and thus machine downtime can be achieved.

By means of a neutral setting-adjustment it is ensured that in the case of a reported position of the servo system in which the hydraulic machine does not produce any delivery flow, no control signal counteracting this state is generated in the servo valve. Otherwise the setting of the control piston in the servo valve does not match the setting of the servo piston in the adjustment device for the hydraulic machine. In such a case machine downtime can never be achieved, since one of the two pistons is always outside of the hydraulic center. A neutral adjustment for the servo valve has the task of centering the control piston in the servo valve in the case of machine downtime in such a way in the control cylinder that through suitable control edge overlaps with appropriate control edge gaps no fluid flows or servo pressures arise that would bring the servo piston of the adjustable hydraulic machine out of balance against the spring forces.

Mechanically actuated servo valves are as a rule controlled via Bowden cables or rod systems in order to regulate the delivery volume of the adjustable hydraulic machine in both delivery directions. This mechanical control should have the most equal reaction possible for both delivery directions. As a result of this the need arises for a symmetrical, that is equally great in both delivery directions but respectively small dead band within which the pump does not produce any delivery volume. Simultaneously the maximum delivery volumes of the two delivery directions of the adjustable hydraulic machine should be achieved in the case of an equally great input signal. In particular for mechanical adjustments this means that the deflection of the control device in one direction should be precisely as great in amount as in the other direction so that the delivery power generated by the adjustable hydraulic machine or received by the adjustable hydraulic machine is equally great for both delivery directions. In particular a forward-reverse driving or a left-right pivoting is to be thought of here, which should take place with the same power. In a known design for a mechanical drive of a servo valve by means of for example a Bowden cable or a rod system a torque acts on an input shaft on the servo valve in order to turn said input shaft in the one or other direction. For different reasons, in particular for safety reasons and for reasons of user friendliness, this input shaft must always autonomously strive to return to its neutral position. By way of illustration the machine operator expects that the deflected control lever autonomously swivels back to the neutral position after being released. This can for example be achieved by a permanently acting spring force in the servo valve.

In the case of a design of such a neutral setting mechanism known from DE 41 25 706 C1the input shaft, which can be turned mechanically in two directions, exhibits a flattened portion upon which a spring-loaded spring-loaded, guided sliding part acts. The sliding part exhibits a likewise planar surface on the contact surface between the flattened portion and the face of the sliding part, as a result of which in the event of the turning of the input shaft from the neutral position a lateral contact on the flattened portion of the input shaft occurs. The outer axial force through the spring action which acts on the sliding part generates an aligning torque on the input shaft. This aligning torque attempts to move the input shaft back to its neutral position in which the two areas, that is the planar face of the sliding part and the planar flattened portion on the input shaft lie flat or planar on one another. In this planar, flat contact the spring action acts directly in the direction of the axis of the input shaft, so that no torque is generated by the spring action. Through the flat contact of the sliding part on the flattened portion of the input shaft, regardless of the direction of rotation of the shaft the sliding part is shifted away from the axis of the input shaft, to be precise always in the same direction against the springs. As a result of that, torque acting in the one or other direction is generated in the case of the deflection of the input shaft. If the deflection torque on the input shaft is lower than the torque which is generated by the shifted sliding part via the flattened portion on the input shaft, the input shaft rotates by itself back to its neutral position. For the setting/adjustment of the neutral position of the servo valve the known design proposes shifting the connecting lever which connects the input shaft to the control piston beyond its eccentric relative to the position feedback device. With this the control piston in the control cylinder occupies a neutral position for the servo adjustment, regardless of the position of the input shaft. The signal forwarded by the position feedback of positioning the adjustment device of the hydraulic machine is thus adapted to the control piston position.

However, with this, since the neutral position of the servo piston in the servo cylinder in most cases does not correspond to the geometric center, the deflection capability of the control piston in one direction is less than the deflection capability of the control piston in the other direction, which in the two delivery directions leads to differing delivery volumes. In the end result this leads to an asymmetrically adjustable hydraulic machine. The greater the position error to be corrected between the servo valve, i.e. the control piston in the control cylinder and the involved levers as well as the involved guides, the greater the asymmetry between the input signal and the delivery flows in both delivery directions. In the process there are different capacities in the one or other delivery direction, since the maximum delivery volumes of the hydraulic fluid which can be achieved in the one delivery direction or other delivery direction are different.

The invention therefore addresses the problem of providing a device for setting the neutral position of servo valves for adjustable hydraulic machines which ensures the neutral position of the control device in the event of machine downtime and in addition guarantees a balance of the delivery volumes in both delivery directions.

The problem addressed by the invention is solved with a neutral setting device in accordance with the features from the characterizing part of Claim 1 by having the guide element supported against the housing in such a way that the guide element is rotatable in the circumferential direction of the input shaft relative to said input shaft. Preferred embodiments are specified in the subsidiary claims dependent on Claim 1.

In order to obtain the balance of the servo valve with respect to a potential dead band and the maximum delivery volume regardless of the neutral setting, the input shaft, the sliding part and the control piston must be aligned jointly and simultaneously to the neutral setting, so that between the control piston and control cylinder the necessary control edge overlaps or the corresponding control edge gaps arise, so that an equally great deflection capability of the input shaft on both sides is retained.

In accordance with the invention this is achieved with a neutral setting device of an adjustable hydraulic machine with a housing, in which an input shaft is pivoted, at which on a first end a torque can be applied for timing the shaft around its central axis. The torque can for example be applied via a control lever. The shaft is preferably arranged with a first end outside of the housing, wherein its second end protrudes into the servo housing. On the second end protruding into the servo valve housing a cylindrical extension is arranged eccentrically to the central axis, parallel to it, said extension being able to move in a circular path with the input shaft. In the servo valve housing there is further arranged an adjustable control piston which with its control edges in cooperation with the control edges of a control cylinder control the fluid openings to a servo piston, said servo piston in turn setting the hydraulic machine with respect to its delivery direction and/or delivery volume. A lever is arranged for transfer of the deflections of the input shaft to the control piston, said lever being connected in an articulated manner with its end to the control piston and with its second end being mounted in an articulated manner at the position feedback device, which transfers the position of the servo piston to the lever. This position is transferred then from the lever to the control piston. Between the two ends of the lever a bearing position is provided for the reception of the cylindrical extension of the shaft, via which the lever can transfer the deflection of the input shaft to the control piston.

Thus, in the event of the deflection of the input shaft the cylindrical extension is moved on a circular path, as a result of which the articulated, in particular rotatable lever mounted on the bearing position likewise moves in a type of circular path, which shifts the control piston in the control cylinder in the servo valve housing. Through the shifting of the control piston in the control cylinder the openings for hydraulic fluid are altered for control of the servo piston, as a result of which the servo piston is deflected in its position and the hydraulic machine is adjusted. With the eccentric arrangement of the cylindrical extension on the shaft a rotary deflection movement on the input shaft is converted to a translational movement of the control piston, with which the adjustable hydraulic machine can be controlled.

In addition a sliding part is arranged in the servo valve housing, said sliding part being held elastically in a guide element and being able to move perpendicular to the axis of the input shaft. The sliding part is elastically mounted in the direction of movement and exhibits on one end a planar face with which the sliding part can be supported against a planar flattened portion on the input shaft. In the process the support through the elastic mounting is pre-stressed. The cooperation of the flat/planar face of the sliding part with the flat flattened portion, which is constructed on the input shaft, in this connection acts in the same manner as is known from the initially described exemplary embodiment from the prior art. The guide element receives the other end of the sliding part and provides a guide perpendicular to the axis of the input shaft for the sliding part. The sliding part can be pushed away against an elastic force from the shaft along this direction of movement or moved by this elastic force to the shaft. If the shaft is turned, the flattened portion of the shaft presses the sliding part against the spring force for example into the guide element, as a result of which a torque against the turning of the input shaft is generated by means of the elastic force via the eccentric contact of the sliding part on the input shaft caused by the turning of the input shaft. If the deflection torque on the shaft is taken away, the aligning torque, which is transferred via the sliding part to the shaft, causes said shaft to return to its neutral position in which the two planar areas lie flat upon one another.

In accordance with the invention the guide element for the sliding part can be turned in circumferential direction of the shaft, as a result of which the neutral position of the servo valve can be adjusted. If the guide element is moved in circumferential direction of the input shaft the face of the sliding part loses its planar contact with the flattened portion on the shaft, as a result of which due to the elastic force a torque acts on the shaft via the sliding part and the shaft follows the movement of the guide element. Simultaneously with this turning of the input shaft the cylindrical journal, which is arranged eccentrically on the shaft, is moved in a circular path, as a result of which in turn the control piston in the control cylinder is adjusted. Thus a neutral position adjustment of the control piston can be performed, wherein a relative shifting of the control piston vis-à-vis the deflection of the input shaft is prevented. With this the balance for the deflection in both delivery directions is preserved, as a result of which also the delivery maximums in both delivery directions remain more or less the same. With this arrangement the control piston can be adjusted in the neutral position important for machine safety, in said neutral position which the adjustable hydraulic machine does not show any delivery volumes, thus is in machine downtime. Simultaneously the autonomously acting control signal feedback system, which is constructed by the two planar areas of the sliding part and the flattened portion on the input shaft, is in its geometric zero position, in which no torque is exercised on the input shaft. From this geometric zero position the input shaft can now be deflected equally wide symmetrically in both directions, as a result of which there are equally great maximums in delivery volume for both delivery directions on the hydraulic machine.

Through the relative rotatability of the guide element and thus of the sliding part guided within a common zero position adjustment, i.e. neutral position adjustment for the servo valve is achieved, in which the input shaft, the sliding part and the control piston are aligned commonly and simultaneously. Thus between the control piston and the servo valve housing, i.e. control cylinder, the control edge overlap on both sides of the control piston or corresponding control edge gaps necessary for machine downtime arise, said control edge gaps guaranteeing a symmetrical application of hydraulic pressure to the servo piston, so that the servo piston does not change the zero position of the adjustable hydraulic machine. According to the customary state of the art in this connection it is possible to work with both negative and positive control edge overlap as long as it is ensured that in the event of required machine downtime the servo piston, which as a rule can have hydraulic pressure applied on both sides, is not shifted from its zero position and both sides have equally great force applied. Thus the invention provides with simple and cost-effective means a robust neutral position setting device which in addition is extremely robust.

Through the independent rotatability of the guide element relative to the input shaft in the event of neutral position adjustment of the control piston in the servo valve the input shaft can simultaneously be adapted to the adjusted neutral position, as a result of which a symmetrical deflection of the input shaft continues to be possible. This neutral position adjustment of the control piston in the servo valve executed preferably during machine downtime takes place by removing the planar face of the sliding part by turning the guide part from the flat recess at the input shaft and thus forcing the input shaft to turn around its central axis, as a result of which the lever, which is moved via the cylindrical pin on the shaft, adjusts the control piston. After completion of the adjustment operation, i.e. after the resetting of the zero position the input shaft is automatically carried along, without imbalances in the servo valve.

In one preferred embodiment a setting screw, which is arranged perpendicular to the axis of the input shaft and perpendicular to the direction of movement of the sliding part in the servo valve, engages on the guide element, as a result of which by turning the setting screw via for example a threaded engagement between guide element and setting screw the guide element can be turned in circumferential direction of the input shaft. Depending on the selection of the thread in the setting screw or in the guide element a more or less precise adjustment can be achieved, wherein the adjustment can be all the more exact, the finer the thread is.

In a further preferred embodiment the setting screw exhibits a spherical extension on its end in contact with the guide element or is constructed nodular or spherical, and engages in a corresponding indentation on a face of the guide element. Such an indentation can likewise be spherically constructed or can also be inserted into the guide element in the form of a trapezoid groove or keyway. The course of the groove is then preferably arranged parallel to the axis of the input shaft. The thread for tightening or loosening the setting screw is then consequently preferably constructed in the servo valve housing,through which the setting screw penetrates. In the process the screw head of the setting screw is accessible from outside the servo valve housing. This likewise applies to the previously cited embodiment.

For both of the previously cited embodiments it applies that the setting screw preferably supports itself on an inside wall of the servo valve housing, as a result of which the guide element is supported vis-à-vis the servo valve housing. Through the elastic prestress between the guide element and sliding part an equally great counter force acts on the setting screw, said force pressing the setting screw on the inside wall of the servo valve housing. In order to achieve a guiding of the setting mechanism, consisting of the setting screw, guide element, sliding part and elastic element in the direction of the axis of the input shaft, preferably a groove or a threading is arranged on the inside wall at which the setting screw is resting, in which said setting element is guided in its axial direction.

Such a notch, groove or thread on the inside wall area of the servo valve housing in this connection only has to be connected sufficiently long that the empirically determining manufacturer tolerances can be compensated by the adjustment range/swivel range of the guide element arising from the adjustment range of the setting screw. As a rule some clockwise and counterclockwise angular degrees should be sufficient with respect to the axis of the input shaft as a normal swivel range for the guide element.

As described above, the neutral position setting for the control piston in the servo valve can take place by moving the lever via the cylindrical extension on the input shaft by turning the input shaft, wherein the lever is supported on the position feedback device, which for this purpose thus forms a counter bearing. If one proceeds from the zero position of the servo piston, thus from machine downtime, in which the hydraulic machine shows no delivery volume, imbalances on the basis of the manufacturer tolerances in the entire adjustment system of the hydraulic machine—servo piston, servo adjustment device, servo valve and its components—can be corrected by turning the guide element in the servo valve via a setting screw to the effect that the inflows and outflows for servo adjustment of the hydraulic machine are symmetrical and thus the machine can be kept idle. If the hydraulic flows which flow through the openings between the control piston and control cylinder in the servo valve are not equally high for the respective delivery direction in the amount, there would be an adjustment in the servo adjustment device, as a result of which the hydraulic machine would be deflected from its zero position. The present invention prevents this and in the process preserves the balance of the servo valve in advantageous manner.

In the case of adjusted neutral position of the servo valve, as stated above, the openings for the application of pressure of a servo adjustment device of a hydraulic machine are symmetrical, i.e. the equal quantity of hydraulic fluid flows through the respective inflows and outflows for the two delivery directions of the hydraulic machine. In the process a positive control edge overlap is also included, in which there is no hydraulic flow on either of the two sides. With this a secure zero position of the servo piston in the servo adjustment of the hydraulic machine can be achieved, which in turn can be safely kept in machine downtime.

The described implementation ensures that in the neutral position the direction of movement of the sliding part, which often also represents the common axis of guide element and sliding part—for example if these are constructed as a rotation-symmetrical body—always has an intersection with the axis of the input shaft running at a right angle to it. In the process the planar areas of the face of the sliding part and those of the flattened portion, which for example is constructed in a recess on the input shaft, lie flat upon one another. In a further preferred arrangement of the elements in the servo valve the axis of the position feedback device is likewise perpendicular to the common axis of the guide element and of the sliding part. Depending on the position of the guide element in circumferential direction of the input shaft in the special case here an intersection arises between the axis of the lever of the position feedback device and the common axis of the guide element and the sliding part. In a theoretical arrangement of the individual elements of the servo valve, thus for example in the case of the theoretical design and development of a servo valve this intersection of the position feedback device could define the zero point of the servo valve with the axis of the guide element and sliding part. From this zero point the guide element can be adjusted clockwise or counterclockwise in order in practice to compensate the production tolerances of the individual parts and ultimately to shift or turn the control piston to a position in which the inflows and outflows on both sides of the control piston are symmetrically constructed.

The position feedback device of an adjustable hydraulic machine generally consists of a lever which is connected to the adjustment device of a hydraulic machine, for example a swash plate of a swash plate axial piston pump or for example to the bent axis of a bent axis hydraulic motor and is carried along with the respective deflection. Normally the position feedback device exhibits a pin which protrudes into the servo valve and is mounted in an articulated manner there in such a way that depending on the position of the deflected hydraulic machine in the servo valve it represents the position of the adjustment element of the hydraulic machine. Simultaneously with the movement of the lever of the position feedback device the lever of the servo valve is moved to adjust the control piston, which in turn has an effect on the position of the control piston in the servo valve. In the process the cylindrical extension on the input shaft, which is arranged eccentrically to the central axis of the input shaft, forms the hub for the lever of the servo valve. If the input shaft of the servo valve is turned, the position of the hub also changes, i.e. the pivot bearing of the lever of the servo valve, as a result of which the position of the control piston is changed. Such a position change of the control piston results in a change in the openings to the servo piston, as a result of which the position of the hydraulic machine is changed.

In the case of the adjustable hydraulic machine the adjustment range is usually limited due to structural presettings or due to strived for optimal operating points so that likewise a stroke limiter of the control piston is to be provided. In the case of the inventive servo valve this can for example take place by means of a stroke limiter, i.e. a movement limitation through a stop between the guide element and the sliding part. If the sliding part can no longer be pressed into the guide element due to the stop, then the input shaft also cannot be turned any further. This can be felt by the machine operator as a mechanical stop. Other embodiments of a rotation stop in conventional manner with for example a journal on the input shaft and a stop in the servo valve housing are in this connection likewise conceivable.

In a further preferred embodiment the sliding part simultaneously assumes an axial guiding of the input shaft by having said sliding part engage in a groove in the input shaft, wherein the areas adjacent to the planar face, which are preferably aligned perpendicular to the axis of the input shaft, fix the input shaft in its axial mobility. If the input shaft is not fixed in axial direction, it can happen that the input shaft is pushed out of the servo valve housing by the hydraulic pressure present in said servo valve housing. To prevent this, for example in the prior art the input shaft is fixed by a cover which is arranged outside of the servo valve housing. In accordance with the invention the axial securing of the input shaft can take place via the sliding part or also via the guide element, which for example then encompasses the input shaft in a peripheral groove. For this purpose preferably fork-shaped extensions are constructed on the guide element, which engage in a peripheral groove of the input shaft. In this connection care is to be taken that the fork-shaped extensions and the peripheral groove of the input shaft do not hamper the rotatability of the input shaft. For both preferred embodiments for axial fixation of the input shaft there is a prerequisite that the guide element and the sliding part in the servo valve housing are likewise fixed axially, i.e. in the direction of the axis of the input shaft or can support themselves against the servo valve housing. To this end for example a suitably designed shoulder can be constructed in the servo valve housing. The setting screw can also be seen as a further support in axial direction, wherein here high forces cannot be transferred. To prevent the input shaft from pressing into the servo valve housing, a shaft shoulder can be provided on the first end of the input shaft which prevents a shifting of the input shaft into the servo valve housing.

In a further preferred embodiment the fork ends of the guide element not only protrude into a peripheral groove on the input shaft, but rather perpendicular to the axis of the input shaft they are implemented so wide that they can likewise engage in a groove which is arranged at the height of the peripheral groove of the input shaft in the servo valve housing. With this the fork-shaped extensions of the guide element engage both in the groove in the input shaft and also in a groove in the servo valve housing and thus serve both as a type of shaft retainer ring to prevent the input shaft from either moving out of the valve housing or into the servo valve housing. Such designed fork ends on the guide element then make a shaft shoulder provided outside of the servo valve housing, as described in the previous exemplary embodiment, superfluous. Fork-shaped extensions, which simultaneously engage in a groove in the input shaft and in a groove in the servo valve housing secure the input shaft in its position so that it only exhibits a degree of freedom, that of turning around its central axis.

If the guide element is designed as previously described, i.e. it encompasses the shaft in a peripheral groove of the shaft and simultaneously engages in a groove or recesses in the servo valve housing, the axial securing task of the sliding part can likewise be omitted, as a result of which frictional forces, caused by sliding the end of the sliding part with the planar face in or out of the recess on the input shaft can be reduced. With this there remains for the sliding part the purely radial direction of movement for fixing the neutral position of the servo valve. With the engagement of extensions of the guide element into the servo valve housing the guide element can simultaneously be fixed in its axial position with respect to the servo valve housing, as a result of which axial forces, i.e. forces in the direction of the input shaft are prevented. If the setting screw is designed with a spherical end within the servo valve housing, and in the servo valve housing on the inside wall, at which the spherical end of the setting screw adjoins, and simultaneously the end of the guide element in which the spherical end of the setting screw engages, are designed nodular or friction optimized, excess contact pressures can be prevented, which leads to an easily accessible adjustability of the servo valve.

For an improvement of the surface feel with respect to the zero position, i.e. neutral position of the servo valve, for example a spring loaded ball can be provided on an adjacent surface of the face of the sliding part in axial direction of the input shaft, which snaps into a corresponding notch of an axial area of the input shaft in the neutral position of the servo valve. Of course this principle can also be reversed, so that the notch is arranged in the sliding part and a spring loaded ball is provided in the input shaft on an axial area. The development of a ball can however also be provided on the face of the sliding part itself, wherein a spherically constructed region of the face of the sliding part engages in a corresponding recess of the input shaft, as soon as the two planar areas lie flat upon one another.

With the present invention a simple, robust and cost-effective possibility is created for providing a servo valve for the adjustment of a hydraulic machine whose neutral position is adjustable, and wherein the balance of the adjustment region of the servo valve is preserved. In the following some exemplary embodiments are shown as examples with the aid of drawings, said exemplary embodiments however are not intended to restrict the scope of protection of the present invention. The figures show the following:

FIG. 1 shows a partially schematic representation of the arrangement of a servo valve of an adjustable hydraulic machine with a neutral position device in accordance with the invention.

FIG. 2 shows a section through a servo valve in accordance with the first exemplary embodiment.

FIG. 3 shows a sectional view of a second exemplary embodiment.

FIG. 4 shows a detailed view of a third embodiment in a partial section.

FIG. 5 shows an embodiment in accordance with FIG. 4 in front view.

FIG. 6 shows a further exemplary embodiment in section through the guide element.

FIG. 7 shows a further exemplary embodiment of the guide element.

FIG. 1 shows a section in lateral view through a servo valve 1 with a neutral setting device according to the invention with a servo valve housing 2, in which an input shaft 3 is pivoted. The input shaft 3 is connected on its upper end 3 a to a control lever 27 and can be swiveled via said lever by an operator in an angular region around the axis 23. On the lower end 3 b of the input shaft 3 a cylindrical extension 25 is constructed, said extension being arranged eccentrically to the axis 23, but parallel to it. The extension 25 engages in a recess in the lever 5 serving as a bearing position 5 c, whose first end 5 a is mounted in an articulated manner in the control piston 4 of the servo valve 1 and is pivotably guided in a delimited angular region. The second end 5 b of the lever 5 is connected to a lever 6 of a position feedback device.

As schematically implied in FIG. 1, the servo valve 1 is connected via pressure lines 24 a, 24 b to pressure cylinders 26 a, 26 b, said cylinders acting on a servo piston 24 of an adjustment device of a hydraulic machine not shown in the figure. The position of the first end 5 a of the lever 5 determines the position of the control piston and with this the pressure conditions prevailing n the pressure lines 24 a, 24 b and thus the position of the servo piston 24, which causes the actual adjustment of the hydraulic machine. The supply of the servo valve 1 and the pressure lines 24 a, 24 b with pressure fluid, customarily hydraulic oil, takes place via connections 28 on the servo valve 1, of which only one connection 28 is shown in FIG. 1 by way of example.

The input shaft 3 exhibits a groove-like recess 7 in its lower region, whose floor area is constructed as a planar flattened portion 7 a. In the recess 7 one end of a sliding part 8 is guided in a sliding manner, said sliding part having a planar face 8 a. The end of the sliding part 8 is dimensioned in such a way that the face 8 a can come into positive contact with the flattened portion 7 a of the input shaft 3, wherein this contact can extend to complete, parallel contact of the two planar areas 7 a and 8 a. The other end of the sliding part 8, shown here as a cylinder, is in accordance with this exemplary embodiment mounted in sliding manner in the interior of a guide element 10 and is pre-stressed vis-à-vis this guide element 10 via the spring 9 in the direction of the axis 23 of the input shaft 3. On an outer face of the guide element 10 an inside taper 12 is constructed, which is in contact for example with a spherical or nodular end 11 a of the setting screw 11. This end 11 a supports itself in addition on a groove 14 on an inside wall area 13 of the servo valve housing 2.

FIG. 2 shows a further section in top view through the servo valve 1 in accordance with FIG. 1 in the height of the axis of the setting screw 3, which is cut here at the height of the recess 7 and therefore appears in the shape of a half moon with the flattened portion 7 a. The flattened portion 7 a is in full, areal contact with the planar face 8 a of the sliding part 8, which corresponds to the neutral position of the adjustment device. Parts of the guide element 10 formed as fork end 15 encompass the input shaft 3 and are supported vis-à-vis said input shaft. With this a lateral fixation of this end of the guide element 10 is given, which however permits a swiveling around the axis 23 of the input shaft 3. In the inside of the guide element 10 a spring 9 is shown, which is constructed as a compression spring and presses the sliding part 8 against the input shaft 3. The setting screw 11 is longitudinally displaceably mounted in the housing 1 via a thread and engages with its spherical constructed end 11 a into the indentation of the Inside taper 12 on the face of the guide 10. The opposite side of the spherical end 11 a of the setting screw 11 is supported in the groove 14 in the servo valve housing 2 so that the guide element 10 with the spring 9 and the sliding part 9 is supported on both ends and the spring 9 can exert pressure on the input shaft 3.

The setting of the neutral position of the operating device 27 of the hydraulic machine takes place via the setting screw 11 in the following way: An adjustment of the setting screw 11, whose end region protruding out of the servo valve housing 2 is formed for the engagement of an adjustment tool, leads to a carrying along of the guide element 10, since its Indentation in the face constructed as an inside taper 12 from the spherical end 11 a of the setting screw 11 is positively and non-positively mounted. This causes a swiveling of the sliding part 8 mounted in the guide element 10 with the planar face 8 a vis-à-vis the input shaft 3. As a result the input shaft 3 is likewise swiveled, since the face 8 a raises from the flattened portion 7 a and generates a torque on the input shaft 3. The swiveling of the input shaft 3 is transferred from the cylindrical extension 25 on the lower end 3 b of the input shaft 3 to the lever 5 for adjustment from its end 5 a in the control piston 4. As a result of this the respective pressure in the pressure lines 24 a, 24 b to the pressure cylinders 26 a, 26 b can be set precisely. The swiveling of the input shaft 3 also shows itself on the control lever 27, which is connected to the upper end of the input shaft 3. This lever can be fixed in a desired position by means of a detachable and lockable connection between the input shaft 3 and the control lever 27 after the neutral setting of the device. This e.g. makes possible an adjustment of the control lever 27 with respect to a scale on a control panel of the hydraulic machine after the setting of the neutral position of the control piston 4 of the servo valve 1 and with it of the servo piston 24.

In the operation of the hydraulic machine the control lever 24 can be swiveled by the operator from the neutral position, which for example can be a central position, to a predefined direction. The swivel angle in known manner predefines the desired reaction of the hydraulic machine by having the control piston 4, which is subsequently shifted, change the flow of the pressure fluid in the pressure lines 24 a, 24 b, as a result of which the servo piston 24 (see FIG. 1) is shifted in one or the other direction. The shifting of the servo piston 24 causes a change in direction and or of the delivery quantity of the pressure fluid in the main circuit of the hydraulic machine, which as a result causes the action desired by the operation.

The swiveling of the input shaft 3 caused by the operator via the control lever 27 also changes the contact of the flattened portion 7 a and of the planar face 8 a of the sliding part 8. Instead of contact over the entire area in the neutral position there is only a linear contact on one side of the two areas 7 a or 8 a. Since the force-transmitting contact line lies off center with respect to the axis 23, the sliding part 8 compression loaded by the spring 9 exerts a torque on the input shaft 3. This torque has the tendency of counteracting adjustments made by the operator and returns the control lever to the neutral position. This reset force must accordingly be overcome continuously by the operator. A release of the control lever 27 leads to an automatic reset of the control lever 27 and with that of the control piston 4 to the neutral position, on the basis of the elastically pre-stressed sliding part 8.

In FIGS. 3 through 5 further similar examples of the invention are shown in accordance with FIG. 2, wherein FIG. 3 shows a cross-section, FIG. 4 shows a top view and FIG. 5 shows a lateral view of details of the essential components for setting the neutral position. These exemplary embodiments differ from the previously described embodiments among other things in the deviating design of the guide element 10 and its connection to the input shaft 3. The same reference numbers are used in these and additional figures for matching parts, as can be seen in FIGS. 1 and 2. In FIGS. 4 and 5 it can be seen that the end of the guide element 10 adjacent to the input shaft 3 is constructed in the shape of a fork in the lower region and for stabilization of its position encompasses a lower part of the input shaft 3 in a cylindrical region 29 of lesser diameter. The ends of the fork 15 extend over an imaginary center plane of the input shaft, so that the guide element 10 is securely guided even in the case of the swiveling of the input shaft 3. In addition the ends of the fork 15 fix the input shaft 3 against an axial shifting from the servo valve housing 2, which could take place under the influence of the fluid pressures in the servo valve housing 2. To this purpose said ends protrude on the one hand into the region 29 with lower diameter of the input shaft 2 and on the other hand support themselves in a correspondingly formed groove 16 (not shown) in the servo valve housing 2.The sliding part 8 is in the case of this exemplary embodiment held in a longitudinally displaceable manner in the cylindrical guide element 10 and is pre-stressed by the spring 9 in the direction of the input shaft 3.

FIG. 6 shows a further constructive variant of the invention in top view of a cross-section, in which the guide element 10 for the sliding part 8 is arranged in its inside and the spring 9 is arranged on the outside of these components. The front end of the sliding part 8 with the planar face 8 a is mounted here in a recess in the form of a groove 16 (not shown) of the servo valve housing 2, surrounding a sub-region of the input shaft 3. The wall of the groove 16 and the front end region of the sliding part 8 are formed in such a way that a swiveling is possible, but a secure guiding of the sliding part 8 perpendicular in the axis 23 of the input shaft 3 is always ensured. In accordance with the exemplary embodiment according to FIG. 6 the front end of the sliding part 8 is spherically formed and penetrates into the recess 7 in the input shaft 3. The walls of the recess 7 stabilize in this connection both the axial shifting of the sliding part 8 and that of the input shaft 3, into whose groove-like recess 7 the sliding part 8 protrudes. The rear end of the sliding part 8 exhibits a bore in which the guide element 10 is mounted in a sliding and longitudinally displaceable manner. The guide element 10 and sliding part 8 are braced against one another by the spring 9 arranged on the cylindrical outside of the sliding part 8. The remaining arrangement and its operation correspond to the previously described exemplary embodiments. In the event of the turning of the input shaft 3 the spherically formed extension 30 of the sliding part 8 remains in engagement with the recess 7, as a result of which the axial fixation of both components is preserved even in the case of the swiveling of the input shut 3.

FIG. 7 shows a further exemplary embodiment of the invention in a top view in section. A detailed view is given of the essential components for setting the position of the input shaft 3. The figure shows a constructive variant of the arrangement according to FIG. 6. The sliding part 8 exhibits a spherical or spherical journal on its front side facing the input shaft 3, which engages in a recess 7 in the input shaft 3 that is formed essentially complementary to it. The front end of the sliding part is as a result mounted and fixed in the input shaft 3. The front region of the sliding part 8 surrounding the journal contains the flat planar face 8 a, which can be in contact with the flattened portion 7 a with the input shaft 3 in its peripheral region. This front region 8 b of the sliding part 8, which exhibits a greater width than the other regions, is guided into a groove 14 in the servo valve housing 2not shown here. This is analogous to the design described with the help of FIG. 6 and likewise serves for axial securing of the relative position of the sliding part 8 and input shaft 3 in the servo valve housing 2.

LIST OF REFERENCE SYMBOLS

-   1 Servo valve -   2 Servo valve housing -   3 Input shaft -   3 a first end input shaft -   3 b second end input shaft -   4 Control piston -   5 Lever -   5 a first end lever -   5 b second end lever -   5 c Bearing position -   6 Lever of a position feedback -   7 Recess of the input shaft -   7 a Flattened portion -   8 Sliding part -   8 a planar face -   8 b front region of the sliding part -   9 Spring -   10 Guide element -   11 Setting screw -   11 a End of the setting screw -   12 Inside taper -   13 Inside wall area of the servo valve housing -   14 Groove in the servo valve housing -   15 Fork end -   16 Groove in the servo valve housing -   17 Groove in the input shaft -   23 Axis of the input shaft -   24 Servo piston -   24 a,b Servo-pressure line -   25 Cylindrical extension -   26 a,b Pressure cylinder -   27 Control lever -   28 Opening -   29 Region of smaller diameter -   30 Spherical Journal -   31 Recess 

1. A neutral setting device (1) of an adjustable hydraulic machine with a housing (2), in which are arranged: an input shaft (3) mounted in the housing (2) with a first end (3 a), at which a torque can be applied for turning the input shaft (3) around an axis (23), and a second end (3 b), at which a cylindrical extension (25) eccentrically parallel to the axis (23) is arranged, an adjustable control piston (4) for opening and closing hydraulic fluid openings for application of pressure of a servo piston (24), which adjusts the hydraulic machine with respect to its delivery volume, a lever (5), with a first end (5 a) and a second end (5 b) as well as with a bearing position (5 c) arranged between the two ends (5 a, 5 b), in which the cylindrical extension (25) of the input shaft (3) engages, wherein the first end (5 a) of the lever (5) is connected in an articulated manner to the control piston (4) and the second end (5 b) of the lever (5) is mounted in an articulated manner on a position feedback device (6), which transfers the position of the servo piston (24) to the lever (5), a sliding part (8), which exhibits a planar face (8 a) on one end, with which it is supported against a planar flattened portion (7 a) on the input shaft (3), wherein the sliding part (8) is elastically prestressed perpendicular to the axis (23) of the input shaft (3) and is held by a guide element (10) in such a way that the sliding part (8) can be moved perpendicular to the axis (23) of the input shaft (3) relative to the guide element (10) and the planar face (8 a) and the planar flattened portion (7 a) in neutral position of the control piston (4) lie flat upon one another, characterized in that the guide element (10) is supported vis-à-vis the housing (2) in such a way that the guide element (10) can be rotated in circumferential direction of the input shaft (3) relative to said shaft.
 2. The neutral setting device (1) according to claim 1, in which the guide element (10) through a setting screw (11) which is arranged perpendicular to the direction of movement of the sliding part (8) and perpendicular to the axis (23) of the input shaft (3) and which supports the guide element with one end (11 a) vis-à-vis the housing (2) and engages in the guide element (10) in such a way that the guide element (10) is rotatable by turning the setting screw (11) in circumferential direction of the input shaft (3) relative to said shaft.
 3. The neutral setting device (1) according to claim 2, in which the end (11 a) of the setting screw (11) in engagement with the guide element (10) is spherical and engages in a corresponding recess (10 a) on the guide element (10) and supports itself in a groove (16) in the housing (2) which is constructed on an inside wall (13) of the housing (2) parallel to the axis (23).
 4. The neutral setting device (1) according to claim 1, in which the guide element (10) exhibits a pot-like bore into which the sliding part (8) is guided and upon whose floor area an elastic element (9) is supported, which prestresses the planar face (8 a) of the sliding part (8) against the planar flattened portion (7 a) on the input shaft (3).
 5. The neutral setting device (1) according to claim 1, in which the planar flattened portion (7 a) is constructed on the input shaft (3) in a recess (7) of the input shaft (3).
 6. The neutral setting device (1) according to claim 5, in which the end of the sliding part (8) is constructed on the face (8 a), providing with the recess (7) in the input shaft (3) an axial guide of the input shaft (3).
 7. The neutral setting device (1) according to claim 1, in which the input shaft (3) exhibits a circumferential groove (20) into which the guide element (10) engages with fork shaped ends (10 a, 10 b), as a result of which the guide element (10) is connected to the input shaft (3) in an axially fixed manner.
 8. The neutral setting device (1) according to claim 1, in which the sliding part (8) exhibits an elastically mounted ball (28) on the end at which the planar face (8 a) is constructed, said ball in neutral position of the control piston snapping into a corresponding recess (30) in the input shaft (3).
 9. The neutral setting device (1) according to claim 1, in which the hydraulic machine is integrated in a closed hydraulic circuit.
 10. The neutral setting device (1) according to claim 1, in which the input shaft (3) can be rotated mechanically or electromagnetically. 